Understanding Phase Stability and Phase Transition of Boron Suboxide Using First-Principles Based Potentials

Boron suboxide (B₆O) is a representative icosahedral boron-rich semiconductors. Most interestingly, such compounds exhibit the potential to repair the lattice defects upon the exposure of high energy irradiation. Coupled with their high hole mobility, this unique self-healing ability makes these materials suitable for applications in nuclear batteries.<br/>Motivated to gain precise control over B₆O synthesis, this work aims to decipher the phase stability and phase transition of B₆O that potentially benefit crystal synthesis especially in the low-pressure regime. Here, we will report a first-principles investigation by combining Density Functional Theory and molecular dynamics. By leveraging Materials Project database, the relative thermodynamics stability of boron oxide compounds over a broad range of stoichiometries and compositional phase diagram were generated. Moreover, first-principles calculations also yielded a training set for the development of a classic B/O potential in the ReaxFF framework, to understand the phase transition (i.e., cooling and melting) of B₆O under variable T, P parameters. Molecular simulations showed that the new force field is significantly improved for the systems representing icosahedral boron compounds. We will also briefly show a new strategy to simulate the phase transition of B₆O by developing a neural network-based potential (NNP) trained from ab initio molecular dynamics (AIMD) simulations. We anticipate that this NNP will enable us to achieve accurate but also computationally affordable potentials for the consideration of B6O crystallization in complex chemical and physical environment in the future.